Getting the Best Out of Stainless Steel Part - III

Stainless steels cannot be passivated unless the steel surface is clean and free from contamination and scale from welding operations.

 

Nitric acid alone can be used to remove light surface iron contamination after which the acid facilitates the passivation of the cleaned steel surface.

Passivation improves the corrosion resistance properties of components made of precipitation-hardened, austenitic, and martensitic steels. Passivation treatments improve the surface condition of stainless steel by dissolving iron that has been imbedded in the surface during forming or machining. If allowed to remain, the iron can corrode and give the appearance of rust spots on the stainless steel.

Passivation, which consists of immersing stainless steel components in a solution of nitric or citric acid without oxidizing salts, will dissolve the imbedded iron and restore the original corrosion-resistant surface by forming a thin, transparent oxide film.

Features

• Maximum stainless steel corrosion protection without plating.

• Superior clean surface.

• Eliminates iron contamination reactions with other materials.

• No rust discoloration.

• Surface prepared for priming and painting.

Essentially, passivation is the removal of free iron from the surface of the steel. This is performed by immersing the steel in an oxidant, such as nitric acid or citric acid solution. Since the top layer of iron is removed, passivation diminishes surface discoloration. While passivation does not affect the thickness or effectiveness of the passive layer, it is useful in producing a clean surface for a further treatment, such as plating or painting. On the other hand, if the oxidant is incompletely removed from the steel, as sometimes happens in pieces with tight joints or corners, then crevice corrosion may result. Most research indicates that diminishing surface particle corrosion does not reduce susceptibility to pitting corrosion.

Passivation refers to the chemical neutralization of the surface - increasing corrosion resistance.

Almost any stainless steel that you can buy has been rolled, machined and/or manipulated with carbon or tempered steel implements. This means that, in general, all of the stainless steel that you will ever buy off the shelf or re-manufacture will have an appreciable amount of steel worked into its surface. Without Passivation iron or iron oxide exists on the surface of stainless steel. When any machining or fabrication operations are performed, the condition is worsened. Aside from iron being deposited by tooling, it is also being entrapped underneath the “skin” created by the mechanical operation. In the metal industry this surface impregnated steel is referred to as "free iron".

This free iron corrodes easily. The corrosion process of iron is a very aggressive reaction. This reaction will in almost all cases start corrosion in the stainless steel. Once started, the corrosion of the stainless will continue to take place without the presence of free iron.

The term "Passivation" is used widely in the stainless steel processing industry.  Many people refer to this oxide surface as a chrome-nickel oxide.

In lay terms, the passivation process removes "free iron" contamination left behind on the surface of the stainless steel from machining and fabricating. These contaminants are potential corrosion sites that result in premature corrosion and ultimately result in deterioration of the component if not removed. In addition, the passivation process facilitates the formation of a thin, transparent oxide film that protects the stainless steel from selective oxidation (corrosion). So what is passivation? Is it cleaning? Is it a protective coating? It is a combination of both. This process is known as passivation. Visit their website to find out more ASTROPAK.COM

Equipment and precautions. Passivation should only be performed by trained, experienced technicians familiar with the potential hazards associated with the science. Safety practices must be fully understood when handling passivation chemicals. Special boots, gloves, aprons and other safety equipment must be used. Tanks, heaters and ventilation, as well as baskets and racks must be appropriately engineered to perform the process. Iron or steel parts or equipment must never be introduced to the process, or the results can be devastating. Furthermore, in order to comply with EPA requirements, the necessary water and air permits and treatment capabilities must be in place. The days of mom-and-pop shops performing passivation in a stone crock in the back of the shop are gone.

Specifications and verification testing. There are a few generally accepted industry specifications available for reference when choosing a passivation process. They offer time, temperature and concentration information and subsequent testing requirements to validate the effectiveness of the process. Many large corporations have developed internal specifications to control their unique requirements regarding passivation and verification testing. Regardless of the situation, it is usually prudent to reference a proven procedure when requesting passivation. By referencing a specification, you do not have to reinvent the wheel. By taking advantage of the experiences of others, both successes and failures, you can eliminate much of the guesswork that would otherwise accompany a new process.

So how do you get the performance you have paid for from high-dollar stainless steel alloys? It boils down to a basic understanding that the passivation process is both an art and a science, and that machining, fabricating and heat treating practices can substantially affect the corrosion resistance of the component. Passivation will enhance the corrosion resistance of stainless steels, but to realize the maximum performance from these high-tech alloys, all parties involved with manufacturing must understand their responsibility in maintaining the integrity of the material throughout the process.

Stainless Steel Maintenance Tools

The Introduction of Stainless Steel Products

A Quick Way To Know How To Choose The Correct Stainless Steel

To find out more about Passivation Click here : http://www.astropak.com/ultra-pass-passivation.php

Getting the Best Out of Stainless Steel Part - II

Importance of post-fabrication treatments 

Apart from some specialized processes, welds in stainless steel always result in some degree of heat tint. Heat tint is essentially an oxidized surface which has a reduced corrosion resistance compared to the parent material. Therefore, the normal practice is to carry out some form of post weld treatment to improve the corrosion resistance.

Details of these procedures can be found at:

Post Weld Cleaning and Finishing of Stainless Steels

Welding and Post Fabrication Cleaning for Construction and Architectural Applications

Good fabrication practice always includes post weld treatment. Failure to do so can give rise to     unnecessary cost of rectification later on.

Importance of segregating carbon and stainless steel

Sometimes "rusting" of stainless steel turns out to be nothing of the kind. It is the rusting of carbon steel which has contaminated the surface of the stainless steel at some point in the production process. Possible sources of contamination from carbon steel include:

      Tools

      Lifting Gear, Ropes, Chains

      Grinding dust

      Cutting sparks

      Wire brushes

Wherever possible, stainless steel and carbon steel should be fabricated in separate areas of the  workshop or better still in separate workshops. Where not possible it is important to clean down machines used for carbon steel before using them for stainless steel. Stainless steel surfaces should be protected with plastic coatings for as long as possible.Visit their website to find out more ASTROPAK.COM

 Importance of site management

It is quite possible for everything to be done well in fabrication, only for the whole project to be spoiled by inappropriate practices on site. The issues outlined in 3. apply just as much to the site installation as anywhere else in the process.

In addition, it must be remembered that what is appropriate for one building material is unacceptable for another. For stainless steel it has to remembered that masonry and brick cleaners may contain hydrochloric acid sometimes called muriatic acid. If these fluids are to be used at all near stainless steel, care should be taken to protect the stainless steel surfaces. If splashes occur, they should be immediately washed off with water. Failure to do so will result in serious attack of the stainless steel resulting in expensive rectification costs

Importance of choosing correct grade for the application

This aspect almost goes without saying. It is only this far down in the list because it usually is    considered. But if the "wrong" grade has been chosen the consequences can be severe. Some guidelines on material selection are given here. 

Cleaning and Maintenance

Some people think that stainless steel's corrosion resistant surface somehow repels dirt and other contaminants. Like any surface stainless steel requires some maintenance. Guidance on this aspect can be found at Cleaning Methods for Stainless Steel

Importance of seeking technical advice in cases of doubt 

If there is any doubt about the correct choice of grade, surface finish or other aspect of a prospect  involving stainless steel, the following advisory services can be consulted: To find out more about passivation stainless steel Click here : http://www.astropak.com/ultra-pass-passivation.php

Getting the Best Out of Stainless Steel Part - I

When we talk about stainless steel, we, naturally, expect it to be stainless. But, some homeowners are very disappointed and complain that products claiming to be made of stainless steel have gone rusty. Have companies cheated on these products?

Not necessarily! Understanding the whole process better will tell us that there are many factors that may have led to this isolated circumstance.

Manufacturers have long known that the surface finish on stainless steel play a crucial role on its corrosion resistance. Without going into technicalities, experts say that among all, surface finishes that are brightly polished provide maximum resistance to corrosion. It has been proven that this kind of compared to common surface finish, can withstand even severe environments where corrosion easily happens, such as heavy urban and coastal areas. 

Armed with this knowledge, the stainless steel industry now manufactures stainless steel in brightly polished finishes. However, this is only possible if stainless steels have undergone a cleaning and decontamination process from the welding process. This process is known as stainless steel passivation. Visit their website to find out more ASTROPAK.COM

People in the steel processing industry are in the know of passivation since it is widely used process in producing stainless steel products. To us outside the industry, it is best to explain passivation as the process in which “free iron” contamination that remained on the surface of stainless steel from machining and fabricating is removed. It is very important to remove these materials because this factor heavily contributes to early corrosion and, eventually, deterioration of the product just like what home owners complain of in their products that are claim to be made of stainless steel. 

Another good thing about this process is it improves the surface area of stainless steel by producing a transparent coating that protects stainless steel from some factors of corrosion. One process with two results is a very beneficial thing for the industry and consumers, as well.

How it is exactly done involves using nitric acid solution where stainless steel components are immersed, to dissolve imbedded iron left behind and facilitate, on the side, a formation of thin oxide film serving as protective covering of the product.

Stainless steel products that have undergone pickling passivation will least likely produce rust discoloration unless some other step in the manufacturing process influences it to be otherwise. It also produces a superior clean surface that’s free from contamination with other materials. It’s also cost-efficient since surfaces are already ready for priming and painting. 

Understanding of everyone involved of the importance of maintaining the integrity of the material in every step of the manufacturing process is essential to produce a material that’s made of best quality for what is expected of it. To find out more about pickling passivation Click here : http://www.astropak.com/pickling-and-passivation.php